A blind prediction experiment was conducted for the strong-motion data recorded at the Turkey Flat test area
during the September 28, 2004 M>6.0 earthquake. The motion was predicted at several sites by 15 prediction
teams, first based on the observed motion at the edge of the valley, and secondly, based on the observed motion
in the rock underlying the valley. Predictions were received from geotechnical firms and researchers, both in
the US and internationally. A workshop was held to preliminarily review and compare the predictions to each
other and the recorded data. In general, the predictions based on the valley-edge motion exceed the observed
data. Predicted peak ground acceleration at the center of the valley exceeded the observed by about 50% and
predicted response spectra exceeded the observed by as much as 35 times at periods near 0.5 sec. In the
second phase, involving predictions based on the recorded motion beneath the valley sediments, much closer
results were obtained. In both phases, the predictions by different investigators were quite similar to each
other. The use of nonlinear vs. equivalent-linear models did not significantly improve the predictions for
this stiff-soil, relatively low strain motion.